With all of their inherent advantages, including immediate strike ability, efficiency, dimmability and many others, LED fixtures have become very common in many applications. LED Light fixtures for use in sports venue/stadium lighting generally have an LED array which is adapted to project light onto the sports venue. These LED fixtures differ from some high bay lighting that might have a roughly similar appearance in that the sports lighting fixtures have a beam angle less than 70 degrees and sometimes as little as 10 degrees. These fixtures are more powerful than other types of fixtures because they are designed to cover large areas with a high light level. These sports light fixtures have support mechanism that allows for very fine control of the aiming as well as compatibility with standard sports lighting poles, cross arms, and platforms. These fixtures differ from fixtures employed in other industries/applications because they must have a very long maintenance-free life because they are commonly very inaccessible when mounted to the top of a 125′ tall light pole. Maintenance at this height becomes very expensive.
The sporting community, however, has been much slower to adopt LED technology. Many sports lighting fixtures can look acceptable when you are standing behind it. However, when you're the athlete searching the night sky for a pop fly or a fan looking across the pitch, it has been found to be different. A major factor in this is the problem of glare. Most new LED sports lighting fixtures are bright enough, but the light quality eliminates them from serious consideration due to the hotspots and glare which has been found to obscure the vision of the spectator and/or competitor. LED Technology's inherent energy savings has been recognized for years. As the technology has matured, those savings have only increased along with the lumen output per watt. At the same time, however, there is a growing concern that the glare caused by the drive for increasing efficiency is making these lights less suitable for sporting venues.
A need exists to reduce or eliminate glare. Glare is excessive and uncontrolled brightness. It is caused by the luminous intensity per unit area of light travelling in a given direction. This can cause visual discomfort and reduced visibility. Fans and players have become very familiar with the uncomfortable sensation. Glare is occurring with greater frequency, especially in sports venues, as manufacturers are doing everything they can to push as much light as possible out of a fixture. They accomplish this by utilizing higher efficiency LEDs and forcing light from those LEDs through small, individual TIR lenses and reflectors. The lenses concentrate the light for better delivery, but inevitably create unacceptable levels of glare. Intense light is forced through hundreds of plastic lenses. Without a significant physical distance between the LED and lens and no reflector shaping, unacceptable levels of glare are inevitable.
Evaluating glare in quantifiable terms can be difficult, but not impossible. It's not simply a measure of lux or foot-candles alone. Instead, one must measure light density over a given area, referred to luminance (how bright it appears to the human eye), which typically is measured in candelas per square meter (cd/m2) or nits. With sports lighting, lumen density per square inch can also be used to show relative glare factor. A common mistake in measuring LED Luminaire luminance is measuring the entire fixture. Luminance must be measured at the luminous opening, in other words at the smallest point (without any breaks) that emits light out of the fixture. If one were to measure the entire LED luminaire, it would not account for the “shards” of light emitted from each individual LED. The light emitted from individual LED luminaire designs is mare akin to a series of laser beams in contrast to the homogenous output of a traditional luminaire.
Many conventional LED sports lights utilize numerous small, plastic TIR lenses which condense and collimate light emitted by LEDs. In practice, such LEDs can produce over 1000 lumens each and can average a lumen density of 1275+ Lumens/sq. in. (with substantially higher peak lumen densities). Such concentrated, ultra-bright points inherently produce very noticeable glare.